Method of treating a used platinum group alumina catalyst with a metal promoter

ABSTRACT

A method for preparing an improved composition of matter whereby a solid catalyst comprising alumina derived from hydrous alumina predominating in alumina trihydrates and at least one platinum group component is used in hydrocarbon conversion service for a period of time to reduce the surface area of said solid catalyst to from about 20% to about 90% of the surface area of the original solid catalyst. This decreased area solid catalyst is treated with at least one metal promoter to produce a treated catalyst having improved properties. An improved method for hydrocarbon conversion using this treated catalyst is also disclosed.

This application is a continuation-in-part application of application,Ser. No. 315,906, filed Dec. 18, 1972, now abandoned.

This invention relates to an improved method for making hydrocarbonconversion catalysts and method for using same. More particularly, theinvention relates to methods for producing catalysts which have improvedproperties and methods for using these catalysts.

Alumina supported metal-containing catalysts have been demonstrated inthe prior art to be useful for catalyzing a wide variety of chemicalreactions. The reactions which are promoted by these types of catalystsinclude hydrocracking, isomerization, desulfurization,hydrodesulfurization, cyclyization, alkylation, polymerization,cracking, hydroisomerization and the like. Integrated processes such ashydrocarbon reforming or hydroforming, hydrocarbon hydrocracking,hydrocarbon isomerization and the like may utilize thesemetal-containing alumina based catalysts.

After a period of time in service, these metal-containing alumina basedcatalysts become deactivated and must be either replaced or regenerated.In order to reduce the frequency of such catalysts replacements orregenerations, it is desirable that these metal-containing aluminacatalysts maintain reasonably high catalytic activity over a protractedperiod in service. In other words, the activity and/or stability of thecatalysts should be maximized.

Therefore, it is an object of the present invention to provide a methodfor producing an improved composition of matter.

An additional object of the present invention is to provide a method forproducing a catalyst having improved activity stability.

Another object of the present invention is to provide an improvedhydrocarbon conversion process.

A still further object of the present invention is to provide a methodfor producing an alumina-based composition containing a platinum groupmetal and at least one additional metal for use as hydrocarbonconversion catalysts. Other objects and advantages will become apparenthereinafter.

Therefore, in one aspect of the present invention, a method has beendiscovered for producing an improved composition of matter comprising amajor amount of alumina, at least one platinum group metal component andat least one stabilizing metal component. The method to produce theimproved composition of matter comprises:

1. contacting a solid catalyst comprising a major portion of aluminaderived from hydrous alumina predominating in alumina trihydrate and acatalytically effective amount of at least one platinum group componentin at least one reaction zone with hydrocarbon in the presence ofhydrogen at hydrocarbon conversion conditions to chemically convert atleast a portion of the hydrocarbon and form carbonaceous deposits on thesolid catalyst;

2. contacting the solid catalyst with an oxidizing atmosphere, e.g., anoxygen-containing gas, to remove at least a portion of the carbonaceousdeposits and form a regenerated solid catalyst;

3. repeating steps (1) and (2) until the surface area of the regeneratedsolid catalyst is reduced to from about 20% to about 90%, preferably tofrom about 40% to about 80%, of the surface area of the solid catalystused in first performing step (1) to form a decreased area solidcatalyst; and

4. treating said decreased area solid catalyst with at least one metalpromoter to produce a treated catalyst having improved properties.

The treated catalyst prepared by the method of the present invention isuseful in an improved hydrocarbon conversion, e.g., hydrocarbonreforming, process. Therefore, another aspect of the present inventionis a hydrocarbon conversion process using the treated catalyst preparedas described above comprising contacting the treated catalyst withhydrocarbon in the presence of hydrogen under hydrocarbon conversionconditions to chemically convert at least a portion of the hydrocarbon.

As indicated above, the solid catalyst utilized in the present inventioncomprises alumina derived from hydrous alumina predominating in aluminatrihydrate and at least one platinum group metal component. Consideringfirst the alumina utilized in the solid catalyst of the presentinvention, it is preferred that this alumina material be a porous,adsorptive, support having a surface area of from about 25 m² /gm toabout 600 m² /gm or more, preferably from about 350 m² /gm to about 600m² /gm. The alumina comprises a major proportion, preferably at leastabout 80%, and more preferably at least about 90%, by weight of thecatalyst. The more preferred catalyst support, or base, is an aluminaderived from hydrous alumina predominating in alumina trihydrate whichalumina, when formed as pellets and calcined, has an apparent bulkdensity of from about 0.75 gm./cc to about 0.85 gm./cc, pore volume fromabout 0.45 ml/gm to about 0.55 ml/gm, and surface area from about 350 m²/gm to about 600 m² /gm. The alumina support may contain, in addition,minor proportions of other well-known refractory inorganic oxides suchas silica, zirconia, magnesia and the like. However, the most preferredsupport is substantially pure alumina derived from hydrous aluminapredominating in alumina trihydrate.

The alumina support may be synthetically prepared in any suitable mannerand may be activated prior to use by one or more treatments includingdrying, calcination, steaming and the like. The alumina may bemacroformed into particles of any desired shape such as spheres, pills,cakes, extrudates, powder, granules and the like using conventionalprocedures known in the art.

The support, i.e., alumina derived from hydrous alumina predominating inalumina trihydrate, may be prepared according to the methods disclosedin U.S. Pat. No. 2,838,444; and 2,838,445; which patents are herebyincorporated herein by reference.

As indicated above, the catalyst of the present invention also containsa catalytically effective amount of at least one platinum group metalcomponent. The platinum group metals include platinum, palladium,rhodium, ruthenium and the like, with platinum being preferred for usein the present invention. The platinum group metal component, such asplatinum, may exist within the unreduced solid catalyst at least in partas a compound such as an oxide, sulfide, halide and the like, or in theelemental state. The platinum group metal component generally comprisesfrom about 0.05% to about 3.0%, preferably from about 0.05% to about1.0%, by weight of the catalyst calculated on an elemental basis.Excellent results are obtained when the catalyst contains from 0.2% toabout 0.9% by weight of the platinum group metal.

The platinum group component may be incorporated in the catalyst in anysuitable manner, such as by coprecipitation or cogellation with thealumina support, ion-exchange with the alumina support and/or aluminahydrogen, or by the impregnation of the alumina support and/or aluminahydrogel at any stage in its preparation and either after or beforecalcination of the alumina hydrogel. The preferred method for adding theplatinum group metal to the alumina support involves the utilization ofa water soluble compound of the platinum group metal to impregnate thealumina support prior to calcination. For example, platinum may be addedto the support by comingling the uncalcined alumina with an aqueoussolution of cloroplatinic acid. Also, the platinum group metal may beadded to the support as a sulfide by comingling the uncalcined supportwith an aqueous solution of a water soluble platinum group metalcompound and a water soluble sulfide, preferably H₂ S. Otherwater-soluble compounds of platinum may be employed as impregnationsolutions, including, for example, ammonium chloroplatinate and platinumchloride. It is preferred to impregnate the support with the platinumgroup metal when the support is in a hydrous state. Following thisimpregnation, the resulting impregnated support is shaped (e.g.,extruded), dried and subjected to a high temperature calcination oroxidation procedure at a temperature in the range from about 700° F. toabout 1500° F., preferably from about 850° F. to about 1300° F., for aperiod of time from about one hour to about 20 hours, preferably fromabout one hour to about five hours.

Certain catalysts of the present invention, e.g., a fully compoundedhydrocarbon reforming catalyst, preferably include a halogen component.This combined halogen may be fluorine, chlorine, and bromine andmixtures thereof with fluorine and particularly chlorine being preferredfor the purposes of the present invention. The halogen may be added tothe alumina particles in any suitable manner either during preparationof the macrosize particles or before or after the addition of thecatalytically active platinum group metal component describedpreviously. In any event, if the halogen is included, it is added insuch a manner as to result in a fully composited catalyst that containsfrom about 0.1% to about 1.5%, preferably from about 0.2% to about 1.3%by weight of halogen calculated on an elemental basis.

The composition comprising at least one platinum group metal componentand alumina derived from hydrous alumina predominating in aluminatrihydrates prepared, for example, by a method set forth above, isgenerally dried at a temperature of from about 200° F. to about 600° F.for a period of from about 2 to 24 hours or more and finally calcined ata temperature of about 700° F. to about 1500° F., preferably from about850° F. to about 1300° F. for a period of from about 1 hour to about 20hours and preferably from about 1 hour to about 5 hours to produce thesolid catalyst.

This solid catalyst is preferably subjected to reduction to insurechemical reduction of at least a portion of the platinum group metalcomponent. Thus, prior to and/or during performance of step (1) of theabove method, it is preferred to contact the solid catalyst (orregenerated solid catalyst) with a reducing medium, e.g., ahydrogen-containing gas, to chemically reduce at least a portion of theplatinum group metal.

The reducing medium may be contacted with solid catalyst at atemperature of about 800° F. to about 1200° F. and at a pressure in therange from about 0 psig. to about 500 psig. and for a period of time ofabout 0.5 to 10 hours or more and in any event, for a time which iseffective to chemically reduce at least a portion, preferably a majorportion, of the platinum group metal component of the catalyst. Bychemical reduction is meant the lowering of oxidation states of themetallic components below the oxidation state of the metallic componentin the unreduced solid catalyst. For example, the solid catalyst maycontain platinum salts in which the platinum has an oxidation statewhich can be lowered or even reduced to elemental platinum by contactingthe unreacted catalyst with a hydrogen-containing gas. This reductiontreatment is preferably performed in situ (i.e., in the reaction zone inwhich the catalyst is to be used), as part of the start-up operationusing virgin unreduced solid catalyst or regenerated (e.g. regeneratedby treatment with an oxygen-containing gas stream) solid catalyst. Also,chemical reduction of the metallic components on the catalyst may occurwhile step (1) of the above process is taking place. The preferredreducing medium for use in the present invention is a gas streamcomprising at least a major portion (calculated on a molar basis) ofhydrogen.

According to the present invention, a hydrocarbon charge stock andhydrogen are contacted with the solid catalyst of the type describedabove in at least one reaction zone to chemically convert at least aportion of the hydrocarbon and form carbonaceous deposits on the solidcatalyst. This contacting may be accomplished by using the catalyst in afixed bed system, a moving fbed system, a fluidized bed system or in abatch type operation. However, in view of the danger of attrition lossesof the valuable catalyst and of well-known operational advantages, it ispreferred to use a fixed bed system. In this system, a hydrogen-rich gasand the charge stock are preheated by any suitable heating means to thedesired reaction temperature and then are passed into at least onereaction zone containing a fixed bed of the catalyst hereinabovecharacterized. It is understood that the reaction system may include oneor more separate reaction zones with suitable means therebetween toinsure that the desired conversion temperature is maintained at theentrance to each reactor. The reactants may be contacted with thecatalyst bed in either upward, downward, or radial flow fashion. Inaddition, the reactants may be in the liquid phase, a mixed liquid-vaporphase, or a vapor phase when they contact the catalyst, with bestresults obtained in the vapor phase.

When the catalysts described herein are used in a hydrocarbon reformingoperation, the reforming system may comprise a reforming zone containingat least one fixed bed of the catalyst previously characterized. Thisreforming zone may be one or more separate reactors with suitableheating means therebetween to compensate for the net endothermic natureof the reactions that take place in each catalyst bed. The hydrocarbonfeed stream that is charged to the reforming system will comprisehydrocarbon fractions containing naphthenes and paraffins that boilwithin the gasoline range. Typically, the hydrocarbon feed stream maycomprise from about 20% to about 70% by weight of naphthenes and fromabout 25% to about 75% by weight of paraffins. The preferred chargestocks are those consisting essentially of naphthenes and paraffins,although in some cases aromatics and/or olefins may also be present.When aromatics are included in the hydrocarbon charge stock, thesecompounds comprise from about 5% to about 25% by weight of the totalhydrocarbon charge stock. A preferred class of charge stocks includesstraight run gasolines, natural gasolines, synthetic gasolines and thelike. On the other hand, it is frequently advantageous to chargethermally or catalytically cracked gasolines or higher boiling fractionsthereof, called heavy naphthas. Mixtures of straight run and crackedgasolines can also be used to advantage. The gasoline charge stock maybe a full boiling range gasoline having an initial boiling point of fromabout 50° F. to about 150° F. and an end boiling point within the rangeof from about 325° F. to about 425° F., or may be a selected fractionthereof which generally will be a higher boiling fraction commonlyreferred to as a heavy naphtha -- for example, a naphtha boiling in therange of about C₇ to about 400° F. In some cases, it is alsoadvantageous to charge pure hydrocarbons or mixtures of hydrocarbonsthat have been extracted from hydrocarbon distillates -- for example, astraight-chain paraffin -- which are to be converted to aromatics. It ispreferred that these charge stocks be treated by conventionalpretreatment methods, if necessary, to remove substantially allsulfurous and nitrogenous contaminants therefrom.

In other hydrocarbon conversion embodiments, the charge stock will be ofthe conventional type customarily used for the particular kind ofhydrocarbon conversion being effected. For example, in an isomerizationembodiment the charge stock can be a paraffinic stock rich in C₄ to C₈normal paraffins, or a normal butene-rich stock or a n-hexene-rich stockand the like. In hydrocracking embodiments, the charge stock may be agas oil, such as heavy straight run gas oil, heavy cracked cycle oil andthe like. In addition, alkylaromatics can be conveniently isomerized byusing the catalyst described herein. Likewise, pure or substantiallypure, hydrocarbons can be converted to more valuable products by usingthe catalyst of the present invention in any of the hydrocarbonconversion processes which are promoted by a platinum groupmetal-containing alumina based catalyst.

In a reforming operation, an effluent stream is withdrawn from thereforming zone and passed through a condensing means to a separationzone, typically maintained at about 100° F. wherein a hydrogen-rich gasis separated from a high octane liquid product, commonly designated as areformate. The resultant hydrogen stream is then recycled by suitablecompressor means back to the reforming zone. The liquid phase from theseparation zone is commonly treated in a fractionating system to adjustits butane concentration and thus control the volatility of theresulting reformate.

The conditions utilized in the numerous other hydrocarbon conversionoperations within the scope of the present invention are thosecustomarily used for the particular reaction, or combination ofreactions, that is to be effected. For instance alkylaromatichydrocarbon isomerization conditions include: a temperature of about400° F. to about 900° F.; a pressure of from 0 psig. to about 1500psig.; hydrogen-to-hydrocarbon mole ratio of from about 0.1:1 to about20:1, and a weight hourly space velocity (WHSV) (calculated as weight ofthe hydrocarbon charge stock contacted with the catalyst per hourdivided by the weight of the catalyst) of from about 0.5 to 20.Likewise, hydrocracking conditions include: a pressure of from about 500psig. to about 3000 psig.; a temperature of from about 400° F. to about900° F.; a WHSV of from about 0.1 to about 10; and a hydrogencirculation rate of from about 1000 to about 10,000 cubic feet perbarrel of hydrocarbon charge stock.

In the reforming embodiment of the present invention, the pressureutilized is selected in the range of from about 50 psig. to about 1000psig., with the preferred pressure being from about 100 psig. to about600 psig. Reforming operations may be conducted at the more preferredpressure range of from about 200 psig. to about 400 psig. to achievesubstantially increased catalyst life before regeneration.

For optimum reforming results, the temperature in the reaction zoneshould preferably be within the range of from about 700° F. to about1100° F. more preferably in the range of from about 800° F. to about1050° F. The initial selection of the temperature within this broadrange is made primarily as a function of the desired octane of theproduct reformate, considering the characteristics of the charge stockand of the catalyst. The temperature may then be slowly increased duringthe run to compensate for the inevitable deactivation that occurs, toprovide a constant octane product.

In accordance with the reforming process of the present inventionsufficient hydrogen is supplied to provide from about 2.0 to about 20moles of hydrogen per mole of hydrocarbon entering the reaction zone,with excellent results being obtained when from about 7 to about 10moles of hydrogen are supplied per mole of hydrocarbon charge stock.Likewise, the weight hourly space velocity, i.e., WHSV, used inreforming may be in the range from about 0.5 to about 10.0 with a valuein the range from about 2.0 to about 5.0 being preferred.

As noted previously, during use of the solid catalyst to promote thechemical conversion of hydrocarbons, a carbonaceous deposit forms onthis catalyst. In order to remove this carbonaceous deposit from thecatalyst, it is necessary to contact the solid catalyst with anoxidizing atmosphere, e.g., oxygen-containing gas and thus form aregenerated solid catalyst. Prior to the solid catalyst being contactedwith an oxidizing atmosphere, the carbon content of the solid catalystis typically above about 0.5 weight percent, often greater than about 3weight percent. The removal of carbon from the solid catalyst may resultin a substantial improvement in the catalytic activity of the solidcatalyst. During the contacting with an oxidizing atmosphere, the carboncontent of the solid catalyst is reduced to below about 0.5 weightpercent, preferably below about a0.2 weight percent. Contacting, e.g.,burning, is conducted by treating the solid catalyst with, for example,a gas containing an amount of oxygen which is controlled to maintain thetemperature of the solid catalyst below about 1000° F., preferablywithin the temperature range of about 700° F. to about 850° F. Thepressure maintained during burning is generally elevated, for instancefrom about 100 psig. to about 500 psig. This controlled burning isusually initiated with an inert gas-containing a small amount of oxygen,for instance up to about 1 mole percent and preferably with an oxygenpartial pressure of at least about 0.2 psia. When the bulk of the carbonhas been removed from the solid catalyst, by a gas-containing arelatively low concentration of oxygen, the amount of oxygen can beincreased to insure that a major portion of the carbon has been removedfrom the catalyst without exceeding the desired temperature. This typeof treatment is exemplified by one or more burn-throughs of thecatalyst, particularly at about 800° F. to about 850° F. and about 100psig. to about 500 psig. with a gas containing above about 1 to about 3or somewhat greater mole percent oxygen. Other suitable carbon burningprocedures can be employed as long as the temperatures are controlledand the carbon level of the catalyst is adequately lowered.

The regenerated solid catalyst formed by contacting the solid catalystwith an oxidizing atmosphere may be treated by additional optionalprocedures to, for example, replenish the halogen content lost duringstep 1 and/or 2 of the present method and/or to reduce the crystallitesize of the platinum group metal on the regenerated solid catalyst.These procedures, for example, the method of U.S. Pat. No. 3,637,524enhance the catalytic activity of the regenerated solid catalyst.

In any event, the regenerated solid catalyst is preferably contactedwith a reducing medium, e.g., a hydrogen-containing gas, in order tochemically reduce at least a portion of the platinum group metal. Thischemical reduction may take place prior to and/or during the time whenthe regenerated solid catalyst is used to promote the conversion ofhydrocarbon as described herein above.

As noted previously, while performing steps 1 and 2 of the presentmethod, the surface area of the catalyst is lowered. Steps 1 and 2 ofthe present method are repeated until the surface area of the solidcatalyst is reduced to from about 20% to about 90%, preferably to fromabout 50% to about 80%, of the surface area of the solid catalyst usedin first performing step 1 of the present method. It has been found thatthe decreased area solid catalyst thus formed may be treated with atleast one metal promoter to produce a treated catalyst having improvedproperties, e.g., improved activity stability.

Included among the metal promoters which may be used in treating thedecreased area solid catalyst are those components comprising rhenium,germanium and iridium. Rhenium and iridium and particularly rhenium aremore preferred as promoters.

Mixtures of two or more of these promoters may also be used. Thesepromoters are normally present in the final treated catalyst in anamount from about 0.01% to about 5%, preferably from about 0.05% toabout 1% by weight calculated on an elemental basis. The treating stepof the present method may be carried out in any suitable manner. Forexample, the procedure for treating the decreased area solid catalystwith a promoter, e.g., rhenium, may involve contacting this solidcatalyst with an aqueous solution of a water soluble compound of thepromoter, for example, rhenium compounds such as perrhenic acid,ammonium perrheneate and the like. Similarly, water soluble iridiumcompounds such as H₂ IrCl.sub. 6 and the like, may be used. The treatedcatalyst may be separated from the aqueous solution and is generallydried at a temperature of from about 200° F. to about 600° F. for aperiod of from about 2 hours to about 24 hours or more and finallycalcined, preferably in the presence of an oxygen-containing gas, at atemperature of about 700° F. to about 1500° F., preferably from about850° F. to about 1300° F. for a period of from about 1 hour to about 20hours and preferably for a period of from about 1 hour to about 5 hours.The treated catalyst is then contacted in a reaction zone with ahydrocarbon in the pressure of hydrogen at hydrocarbon conversionconditions to chemically convert the hydrocarbon as describedpreviously. Unexpectedly, it has been found that the treated catalystdescribed above have improved properties, e.g., improved activitystability relative to the original solid catalyst.

The treated catalyst having improved properties is preferably contactedwith a reducing medium, e.g., hydrogen-containing gas in order tochemically reduce at least a portion of the platinum group metal andmetal promoter prior to and/or during use in the conversion ofhydrocarbons. The treated catalyst is contacted with a reducing mediumin a manner similar to that described previously for contacting thesolid catalyst with a reducing medium.

EXAMPLES 1 and 2

These examples illustrate some of the improved properties of the treatedcatalysts produced by the present invention.

A commercially available catalyst comprising platinum and aluminaderived from hydrous alumina predominating in alumina trihydrates alsoselected for testing. This solid catalyst was in the form of extrudates(cylinders about 1/16 in. in diameter by 1/4 in. long). This catalystcontained about 0.35% by weight of chlorine and 0.35% by weight ofplatinum, calculated on an elemental basis, and 3.25% by weight ofvolatile matter. The surface of the alumina support of this virgin solidcatalyst was 429 m² /gm.

A second commercially available catalyst was also tested. This solidcatalyst was similar to the commercially available catalyst comprisingplatinum and alumina except that it contained about 0.35% by weight ofrhenium and about 1.1% by weight of chlorine calculated on an elementalbasis.

The commercially available platinum-alumina catalyst was employed in ahydrocarbon reforming service using a typical mid-continent naphthafeedstock at temperatures ranging from 857° F. to about 960° F., WHSVranging from 1.8 to 2.0 and hydrogen to hydrocarbon mole ratios rangingfrom 6.5 to 7.5. Prior to being contacted with this hydrocarbon, thevirgin solid catalyst was contacted with a hydrogen-containing gas tochemically reduce at least a portion of the platinum. After a period oftime in hydrocarbon reforming, the solid catalyst was regenerated bycontacting the catalyst with an oxygen-containing gas to burn off thecarbonaceous deposits which had formed during the reforming service.After these carbonaceous deposits had been burned off, the catalyst wasagain contacted with the reducing medium, i.e., a hydrogen-containinggas, to chemically reduce at least a portion of the platinum and thenput into hydrocarbon reforming service.

This procedure was continued until it was determined that the aluminabase on this used catalyst had a surface area of about 236 m² /gm. Thisused catalyst was vacuum impregnated with an aqueous solution ofhydrochloric acid and perrhenic acid. The catalyst solution was allowedto stand overnight. This mixture was then dried at 230° F. for about 16hours and calcined for 3 hours at 900° F. to form the treated catalyst.This treated catalyst contained 0.35% by weight of platinum calculatedon an elemental basis, 0.35% by weight of rhenium calculated on anelemental basis and 1.15% by weight of chlorine calculated on anelemental basis at 4.08% volatile material.

The two virgin solid catalysts and the treated catalyst were performancetested in hydrocarbon reforming service (after conventional contactingwith a hydrogen-containing gas to reduce at least a portion of themetallic components) using a typical mid-continent naphtha feedstock at950° F., 4.0 WHSV and a mole ratio of hydrogen to hydrocarbon of 3.Results of these tests are as follows:

    ______________________________________                                                                 Ex. II                                                                        Platinum-                                                          Ex. 1      Rhenium                                                            Platinum-  Alumina                                                            Alumina    Virgin    Ex. II                                                   Virgin Solid                                                                             Solid     Treatment                                  Catalyst      Catalyst   Catalyst  Catalyst                                   ______________________________________                                        Initial Research                                                               Octane Number                                                                 (clear)      96.6       100.0     100.7                                      Aging Rate, Research                                                          Octane Number per                                                             100 hours     5.6        3.7       2.4                                        Standard Aging Rate*                                                          Research Octane                                                               Number per 100 hours                                                                        8.4        3.7       2.2                                        ______________________________________                                         *Based upon data correlation techniques known to give reasonable              predictions, of commercial catalyst aging behavior.                      

These results indicate a significant increase in the activity stabilityof the treated catalyst prepared by the process of the presentinvention. For example, the standard aging rate of the treated catalystis more than 31/2 times greater than the standard aging rate for thevirgin catalyst comprising platinum and alumina derived from hydrousalumina predominating in alumina trihydrates.

In addition, it has been unexpectedly found that the treated catalyst issignificantly more stable than is a virgin catalyst comprising platinum,rhenium and alumina derived from hydrous alumina predominating inalumina trihydrates.

EXAMPLE IV

This example illustrates the production of an improved compositioncontaining iridium according to the present invention.

A sample of the used platinum-alumina catalyst described previously wasvacuum impregnated with an aqueous solution of hydrochloric acid,ammonium hydroxide and H₂ IrCl₆ having a pH of about 5.5 The catalystsolution mixture was allowed to stand overnight. This mixture was thendried at 230° F. for about 16 hours and calcined for 3 hours at 900° F.to form the treated catalyst. This treated catalyst contained 0.35% byweight of platinum calculated on an elemental basis, 0.10% by weight ofiridium calculated on an elemental basis, and 1.15% by weight ofchlorine calculated on an elemental basis at 3.7% by weight volatilematerial.

This treated catalyst was performance tested in the same manner as thecatalysts of the previous examples. Test results, compared to theresults from Example I, are as follows:

    ______________________________________                                        Catalyst         Example I   Example IV                                       ______________________________________                                        Initial Research 96.6        102.0                                             Octane Number                                                                 (clear)                                                                      Aging Rate, Research                                                                           5.6         3.1                                               Octane Number per                                                             100 hours                                                                    Standard Aging rate*                                                                           8.4         2.4                                               Research Octane                                                               Number per 100 hours                                                         ______________________________________                                         *Based upon data correlation techniques known to give reasonable              predictions of commercial catalyst aging behavior.                       

These results show clearly the superior activity stability of a catalystcontaining platinum and iridium prepared according to the presentinvention relative to a commercially available platinum-aluminacatalyst.

While this invention has been described with respect to various specificexamples and embodiments, it is to be understood that the invention isnot limited thereto and that it can be variously practiced within thescope of the following claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A method for producing acomposition which comprises:1. contacting a solid catalyst comprising amajor portion of alumina derived from hydrous alumina predominating inalumina trihydrate and a catalytically effective amount of from about0.05% to about 3.0% by weight of at least one platinum group metalcomponent calculated on an elemental basis in a reaction zone with ahydrocarbon in the presence of hydrogen at hydrocarbon conversionconditions to chemically convert said hydrocarbon and form carbonaceousdeposits on said solid catalyst;
 2. contacting said solid catalyst withan oxygen-containing gas to remove at least a portion of saidcarbonaceous deposits and from a regenerated solid catalyst; 3.repeating steps (1) and (2) until the surface area of the regeneratedsolid catalyst is reduced to form about 20% to about 90% of the surfacearea of the solid catalyst used in first performing step (1) to form adecreased area solid catalyst; and (4.) treating said decreased areasolid catalyst with a rhenium component to produce a treated catalystcontaining from about 0.01% to about 5% by weight of said rheniumcalculated on an elemental basis having improved catalytic activitystability relative to said solid catalyst first used in step (1).
 2. Themethod of claim 1 wherein said treated catalyst comprises from about0.05% to about 3.0% by weight of at least one platinum group metalcalculated on an elemental basis, and from about 0.1% to about 1.5% byweight of at least one halogen calculated on an elemental basis.
 3. Themethod of claim 2 wherein steps (1) and (2) are repeated until thesurface area of the regenerated solid catalyst is reduced to from about40% to about 80% of the surface area of the solid catalyst used in firstperforming step (1) to form a decreased area solid catalyst.
 4. Themethod of claim 3 wherein said platinum group metal is platinum and saidhalogen is chlorine.
 5. The method of claim 1 wherein step (4)comprises:A. contacting said decreased area solid catalyst with anaqueous solution comprising at least one water-soluble compound of saidrhenium to add at least a portion of said rhenium to said decreased areasolid catalyst; and B. calcining said decreased area solid catalyst toform said treated catalyst.
 6. The method of claim 4 wherein step (4)comprises:A. contacting said decreased area solid catalyst with anaqueous solution comprising at least one water-soluble compound of saidrhenium to add at least a portion of said rhenium to said decreased areasolid catalyst; and B. calcining said decreased area solid catalyst inthe presence of an oxygen-containing gas to form said treated catalyst.